Side-chain conformations in the isomorphous polyfluorinated {4,4′-bis[( 2,2-difluoroethoxy)methyl]-2,2′-bipyridine-κ2 N, N′}dichloridopalladium and -platinum complexes

The polyfluorinated title compounds, [MCl2(C16H16F4N2O2)] or [4,4'-(HCF2CH2OCH2) 2-2,2'-bpy]MCl2 [M = Pd, (1), and M = Pt, (2)], have -C(H-)(2)OC(H-)(2)CF2H side chains with H-atom donors at the alpha and beta sites. The structures of (1) and (2) are isomorphous, with the nearly planar (bpy) MCl2 molecules stacked in columns. Within one column, pi-dimer pairs alternate between a pi-dimer pair reinforced with C-H center dot center dot center dot Cl hydrogen bonds (alpha, alpha) and a pi-dimer pair reinforced with C-H-beta center dot center dot center dot F(-C) interactions (abbreviated as C-H center dot center dot center dot FC, C-H center dot center dot center dot F-C). The compounds [4,4'-(CF3CH2OCH2)(2)-2,2'-bpy]MCl2 [M = Pd, (3), and M = Pt, (4)] have been reported to be isomorphous [Lu et al. (2012). J. Fluorine Chem. 137, 54-56], yet with disorder in the fluorous regions. The molecules of (3) [or (4)] also form similar stacks, but with alternating pi-dimer pairs between the (alpha, beta; alpha, beta) and (beta, beta) forms. Through (C-) H center dot center dot center dot Cl hydrogenbond interactions, one molecule of (1) [or (2)] is expanded into an aggregate of two inversion-related pi-dimer pairs, one pair in the (alpha, alpha) form and the other pair in the (C-H center dot center dot center dot F-C, C-H-beta center dot center dot center dot center dot F-C) form, with the plane normals making an interplanar angle of 58.24 (3)degrees. Due to the demands of maintaining a high coordination number around the metal-bound Cl atoms in molecule (1) [or (2)], the ponytails of molecule (1) [or (2)] bend outward; in contrast, the ponytails of molecule (3) [or (4)] bend inward.